Enkephalin is a natural opiate receptor agonist and is believed to be a mixture of two pentapeptides: H--Tyr--Gly--Gly--Phe--Met--OH (methionine-enkephalin), and H--Tyr--Gly--Gly--Phe--Leu--OH (leucine-enkephalin). Hereinafter, the name enkephalin is used generically to embrace all such compounds.
It has been reported by Beluzzi et.al., Nature, 260, 625 (1976), that when enkephalin is injected into the brain ventricle of rats, a profound analgesia is obtained. It is also known in the art that enkephalin is acted upon by a group of enzymes known generically as enkephalinases, which are also naturally occurring and is inactivated thereby. The present invention provides a method for inhibiting the action of enkephalinases, and compounds useful for accomplishing said method.
The following European Patent Application Nos. 81102770.5, 82108858.0, and 82402314.7 (publication Nos. 38046, 75334 and 82088, respectively) disclose certain phosphorous containing compounds which are described as possessing enkephalinase-inhibiting activity.